While K dot most def is the goat of his generation I've heard maad songs in which he didn't have the best verse, mostly club type of songs etc like fukkin Problems and also I was surpassed that he probably had the weakest verse on 1 train.
I feel that when he just gets to send in his verse and not control the track, extend his verse, re-produce his part etc it's not a given that he'll kill it.
Ludacris is the rapper whom I think has the highest killing percentage, Eminem in his prime, Jiggaman pre retirement age and still to this day when I think about it, Big Boi & 3 stacks..